Everything but the engine

While an economical engine is the heart of a fuel-efficient vehicle, all other components contribute as well. From tires to body styles, here is a look at vehicle technologies that save fuel.

Much has been written about the advancements made to the traditional internal-combustion engine to attain greater overall vehicle efficiency. Not surprisingly, improving efficiency requires looking at many other contributions and the vehicle system as a whole. A number of studies show that a conventionally fueled car uses only 12-15% of its available energy to move. The rest is wasted.

Understanding where that waste energy goes is by no means an exact science. The vast bulk of losses are through thermal and chemical inefficiencies in the combustion process. Estimates for these losses vary anywhere from 60-80%. Smaller amounts are lost in engine idling (10-17%) and powering accessories such as windows or steering (2-3%). Drivetrain components, particularly transmissions, account for about 5-7%. The remaining available power needs to overcome aerodynamic drag, rolling resistance, and inertia.